Lighting control system



A. R. LOCKE LIGHTING CONTROL SYSTEM Nov. 26, 1940,

FildJuly 5, 1952 2 sheets-shes; 1

' VE DE 16%??? fjoczfe No'v. .26, 1940.

A. R. LOCKE LIGHTING CONTROL SYSTEM- Filed July 5, .1932

I 2 Sheats-Sheet 2' POCKET BORDi-IR n 2 iaonosam FOOT N| 5,0

1z BORDER N 1.

FOOT N"! V 45 master control.

Patented Nov. 2c, 1940 UNITED STATES- 2,222,811 LIGHTING com'aor, ssrram Albert R. Locke, Oak Park, 111.; asslgnor or one. half to MonadCorporation, a corporation of Illinois Application July 5, -1932, Serial No. 820,843

' 41 Claims.

This invention relates to improvements in control systems forregulating, as desired, variouscharacteristics in electrical circuits,the invention being especially applicable for the control 5 or visualscenic effects for theater illumination, although the invention ishighly desirable for similar power distribution' installations, and willhave many and various uses and purposes as will be apparent to oneskilled in the art.

1 The invention herein described relates to improved means for carryingout the invention disclosed in my application entitled Selective circuitsystem and remote control, filed June 25, 1928, Serial No. 288,214, forthe reissue of Letters Patent No. 1,638,774 and also relates to a systemand method of operation including features oi connection,advantages,-and principles not set forth in my aforesaid patent.

One distinguishment oi the invention herein described over that setforth in my above identifled patent, is that this invention not onlyteaches the system for and method of preselection of loads, which istaught in that patent, but also teaches the system for and method ofpreselecting and overlapping of intensity control to produce blendingand new lighting eifects.

An object oi this invention is to provide a system in which a pluralityof combinations of lights, or groups of lights for a scenic effect, maybe preselected in independent circuits-for subsequent collectiveenergization, the invention contemplating not only the preselection ofthe various circuits but also the'preselection of the intensity oi thelights in each circuit.

, Another object 01 this invention is to provide I a system by which aplurality of combinations of lights may be preselected for subsequentcollective energization, together with a preselection 0! the intensityat which each circuit is to 40.be subsequently energized, theintensities not g necessa'rily being the same for all the circuits,'

land whereby any preselected combination of circuits may be completelycontrolled as to energization and intensity by means of a unitary Stillanother object oithis invention is the provision oi a system by which aplurality of Y preselected groups of lighting circuits may each becontrolled both as to energization and intensity of energization by amaster control connected in common with its respective group, the

system being such that several master controls may be in circuitsimultaneously with the same single, lighting circuit or same groupcircuits.

of lighting It is also an object or this invention to provide a. systemby which a plurality of preselected combinations of lighting circuitsmay be controlled each by a master controlconnected in common with itsrespective combination of lighting circuits, and in which the control ofany single lighting circuit or plurality 01' lighting circuits may betransferred from one master control to another without any undesiredvariance in the brilliancy or intensity of the m lighting circuit. a

It is another object of this invention to provide a system in which aplurality of load circuits may be preselected for energization andintensity control thereof by a master control, 15 and a differentcombination of load circuits may be likewise preselected for control bya different master control, and so on ior as many master controls as maybe desired, and the master controls maybe utilized ,ior energizing andcon- 20 trolling their respective group of lighting'circuits in anydesired order, or twoor more controls may be in live circuitssimultaneously, some of the load circuits being common to both mastercontrols, without any change in the visual charg5 acteristics oi theload circuits that is not indicated in advance .by the layout of themeans for accomplishing the preselection.

Still another object of this invention is the provision or a system inwhich a plurality of so diflerently colored lighting circuits as a groupmay be preselected by controls individual to each circuit forenergization each at a preselected intensity to produce a predeterminedshade or blending, and saidgroup of circuits may be 001- as lectivelycontrolled by a master control. A still iurther object of this inventionis the provision oi a system in which a plurality of difierent controlsmay each be utilized to control the intensity of the lighting circuit,the sys- 4 tem being such that the intensity eflected by one of saidcontrols may be overlapped with that or another or many other controls,and the re sultant intensity oi the circuit is governed solely by thatcontrol which is at the higher inten- 45 sity. Inother words. the.efiects'of the various controls in live circuit with the lighting unitat the same time are not cumulative, but the circuits may be controlledby that control which is set for the higher intensity as it that control50 was the only one in live circuit tor the lighting unit.

It is alsoan object of this invention to provide asyster'n in which aplurality oi lighting units may be preselected for energization at acertain 56 r intensity for each unit, the intensities not necessarilybeing the same, by a control individual to each unit, and the entirecombination of preselected fighting units may be controlled as toenergization and intensity by means of a master control in commonconnection with all of the individual controls, the intensities of thelighting units varying proportionately as a result of the control by themaster either up or down, whereby the same shade produced by variouslycolored lighting units may be maintained even though the units have beenpreset for different intensities by the individual controls.

Also an object of this invention is the provision of a system in which aplurality of lighting units may be preselected for intensity control bymeans of a control individual to each lighting unit,

which individual controls may be utilized in their individual capacityor selectively connected to a master control.

Another object of this invention is the provision of a system in which aplurality of lighting units may be preselected each as to energizationand intensity by a control individual to the respective units, and allof the preselected units may be selectively varied from a maximum to aminimum intensity by means of a master control exercising a commoncontrol overall of the preselected units, one of the said limits ofintensity for each unit being predetermined by the setting of thecontrol individual to that unit.

It is also an important object of this invention to provide a new andnovel method for illuminat ing with electric lighting circuits.

While some of the more salient features, characteristics, advantages andmethods of the present invention have been above pointed out, otherswill become apparent from the following disclosures.

The invention includes these and other featules of arrangement andoperation, hereinafter described, and shown in a preferred form on thedrawings, as more particularly indicated by the claims.

On the drawings:

Figure 1 is a schematic diagram of an electric system, includingprinciples of the present invention.

Figure 2 is a schematic diagram of an electric system embodying aplurality of set-ups similar to that shown in Figure 1, it beingdistinctly understood that Figure 2 is not limited to the num ber oflighting circuits and the particular number of individual controls andmaster controls shown in the figure, but that the numbers of theserespective parts may be multiplied as desired, this figure being shownin-the simplified Control system, Serial No. 611,337, filed May Thecontrol winding 5 is connected in the plate circuit of a pair ofthermionic tubes l6 and I1 which control the flow of current through thecoil and affect the reactance of the reactor to control the dimming ofthe lamps in the load circuits for lighting eifects in theaters and thelike.

The tubes l6 and I1 are energized through a transformer l8 which has itsprimary winding l9 connected to the supply line l0. Each tube has a'cathode 20, a control grid 2|, and a plat or anode 22.

The cathode of tube It is energized by a secondary winding 23 of thetransformer and the cathode of tube I1 is energized by another secondarywinding 24, and a wire 25 connects the ends of the two secondarieshaving like polarity.

The plates 22 of both tubes are connected in parallel and are fed by asecondary winding 26 of the transformer IS in series with the controlcoil 5. One end of the secondary winding 26 is connected to the wire 25.A condenser I5 is preferably connected across the control coil I5.

The grids of the tubes l6 and are supplied with potential fromtransformers 21 and 28, respectively, connected to the supply lines Ill.

A secondary winding 29 of the transformer 21 is connected through awinding 30 of a reactor 3| to a variable reactor 32 and a resistor 33connected in series between the transformer secondary leads 34 and 35.The control grid of the tube H is connected by a lead 34 to the junctionpoint 31 of the reactor 32 and the resistor 33.

When the reactance of reactor 32 is varied the potential of the point3'! and of the grid is varied in value and in phase relative to thecathode and anode potentials of the tube. When the reactance of thereactor 32 is at its maximum value the potential of point 31 is least,and the plate current of the tube is of maximum value and consequentlythe reactance of the load reactor |2 is least and the lamps II arebrightest.

The method of controlling the impedance of the reactor |2 by the gridpotential of the tube is also described in my copending applicationalready referred to.

The impedance of the load reactor I2 is also controllable by the tube l8having its grid connected by a load 38 to the junction point 39 of avariable reactor 40 and a resistor 4| connected by leads 42 and 43through a winding 44 of a reactor 45 to the secondary of the transformer28.

The manner in which the load reactor is controlled by tube IB is similarto that described in connection, with tub H.

A conductor 25 connects conductors 34 and 43 to conductor 25, tocomplete the grid-filament circuit of the tubes I6 and l1. 4

In order that the impedance of the load circuit that is fed by thetransformer '21 in series with the reactor 3|, or other suitable voltagecontrol means may be maintained substantially constant or withindesirable operating values, a recircuit of the tube I! will, of course,ailect the impedance of the circuit comprising the resistor 33'and thereactor 32, but this change may be compensated for in the adjustment ofthe values of the reactance of the reactor 32.

In supply circuit B, a resistor 4| and a recuit comprising the resistor4| and the reactor.

for controlling the voltage of the supply lines,

may be kept within permissible operating limits to permit simple meansfor the control of said series voltage control means.

It will be understood that in stage lighting many load circuits, orgroups of lamps, are employed, and that the groups are dimmed, darkened,turned to full brightness many times during a pert'ormance. For the sakeof clearness only one group of lamps has been shown, and

the leads 36, 35, and 43 havebeen extended to indicate that a pluralityof control units and load circuits may be controlled by 'the masterswitch means to be described;

The scene lights or groups are preset by the switchboard operator sothat by manipulating a master switch at the proper moment many groups oflights are immediately switched out, in, or dimmed by a single movementof the master switch. For example, for a subsequent scene it is desiredthat upon the movements of a master switch a number of groups of lampswill be simultaneously afiected, some to dim, some to dark, and some tofull brightness. The operator presets his controls by suitably adjustingthe variable reactors 32 of control supply A, for instance,

and at theproper moment switches the control from supply B to supply Ato obtain a new lighting efiect. While the groups arenow controlled 45by control supply A he may produce new lighting efi'ects .by varying thepotential supply A and variously affecting the grid potential of thetubes connected withthat supply.

- To enable the operator to conveniently vary the potential of thesupply A, the reactor 3| is provided with a control winding 41, andvariable resistors 48 and 49 may be connected across the winding by atwo-way single pole switch 5!).

It will be obvious that if the resistors 48 and 89 are preset todifferent values of resistancesthe impedance of the reactor 3| will havedifferent values of impedance as one or the other of the resistors areswitched across the control coil 41.

If the variable reactor 32 is adjusted formini- Y mum reactance thenvariations in the impedance It will now be apparent that with severaldif-v v ferent settings of the grid control reactors-of the 75 severalload controlling groups connected to the stant so that the reactor 3|,or other series means.

supply A, selective control of each group of a number of groups isobtained by simple manipulation of the master switch 50.

Selective control of the tubes connected to sup' ply B is similarlyobtained by manipulation of a two-way single pole switch to connecteither of two variable resistors 52 and 53 across a control winding 54of the reactor 45.

It'will now be clear that the means described enable the operator topreset his controls so that by the manipulation of two simple switchesfour diflerent scenic efiects are obtainable.

An important result obtainable by the instrumentalities described isthat of an overlapping intensity control of the load circuits. Thus,with switch 5| closed and switch 50 open so that the scenic effects ofthe groups of load circuits is, determined by the tubes connected tosupply B, switch 50 may be closed and then the tubes connected to supplyA now contribute in determining the new scenic efiects obtained, andthen switch 5| may be opened to leave supply A alone to determineanother new scenic efiect.

This overlappingoi onecontrol system on the other as a scenic eflectdetermining factor is accomplished without the opening of any gridcircuit and without any break in the continuity of the change from onescenic eiiect to another,

that is, the change takes place smoothly without any transient andunwanted dipping and recovery of the load voltage.

In employing two tubes to control a single load circuit, there is, inaddition to the advantages heretofore stated, the further importantadvantage that failure of one of the tubes does not put the load circuitout of control of the operator Referring now to Fig. 2, this figure alsosh ws two control supplies A and B to determine the illumination andscenic efi'ects' of the group of load circuits for scenesA and B. Fourload circuits, or, in the parlance of the art, individuals are shown,identified as Foot, Border Number 1, Border Number 2, and Pocket lights.These individuals are. each controlled by two thermionic tubes whichcontrol the impedance of a reactor in series with the load circuits;connected to the alternating current supply mains and efiect the reactorin the manner already described in connection with Fig. l.

The grid control supply for scene A includes a transformer 55 connectedto the alternating current mains 56 and having its secondary winding 51connected to leads 58' and 59. A poten- The tubes are tiometerdevice'Sll is connected across the secondary winding, and its movablecontact arm 6| is connected to a lead 82.

To control the grid potential of a thermionic tube 63, governing theFootlight circuit, a potentiometer device 6.4 is connected to the leadsBland 62 and another potentiometer device is connected to the leads 58and 59, the contact v arms of the two potentiometers being connectedometers 64 and 65 is variable by movement of a tact arm on each of thepotentiometers so that, ii desired, when the operator moves the switchmember 66 to the lights-out position there is still enough potential onthe grid of the tube 63 to adjust the load circuit so that the lampfilaments are dull red. By this means the operator may adjust thetemperature of the lamp filaments for the lights out position, and varythe grid -member 61 which rigidly connects a movable conexcitation asthe size of the light unit in the load circuit is changed. The lightingunit filaments may thus be preheated so that when the unit is suddenlyswitched to full brilliancy the filament is not injuriously afiected bythe change in temperature.

The control grid 68 of the tube 63 is connected by a lead 69 to atwo-way switch 10 for switch ing to the potentiometer device 64 or tothe potentiometer device 65. When the grid 58 is connected to thepotentiometer device'65, it is then independent of the potentiometermaster switch 6| so that while other load circuits connected to thetransformer 51 may be variously afiected by adjustment of thepotentiometer master switch 5|, its own load circuit is unaffected.

When the grid 68 is connected to the potentiometer device 64 then it isaffected by move ment of the potentiometer master switch 6| in commonwith other grids similarly connected, so that it is proportionally andselectively affected relative to other grids similarly connected.

It will be apparent that the other individual lighting units, or loadcircuits may be connected to the control supply A for control by, orindependent of, the master switch 6|, after the manner just described inconnection with-the Footlight circuit.

The control means of the supply B for scene B are similar to those ofsupply A. They include a transformer ll having-a secondary 12 connectedto leads l3 and H. A master switch 15 of the potentiometer type having amovable contact switch arm 16 is connected between the leads I! and I4,and a lead 11 is connected -to the arm I6.

A potentiometer device 18 is connected to the leads I3 and I1, and apotentiometer device 19 is connected to the leads I3 and I4, the contactarms of both potentiometers being rigidly connected by a member forsimultaneous movement as indicated at 80.

Like in potentiometers M and 65, provision is made in the potentiometersI8 and 19 for preheating the filaments of the lighting units by movementof a control member 8|, to vary the resistance of the end portions ofthe potentiometers.

A switch 82 is provided so.that a control grid 83 of a thermionic tube84 may be connected alternately to the potentiometers l8 and I9.

A conductor 85 connects conductors and 13 with the filaments of-thecontrol tubes to complete the grid-filament circuit of the tubes.

Recapitulating to some extent, while scene A isbeing produced and thelighting units are being controlled by the supply A, the operatorpresets the intensity of illumination desired for scene B, the masterswitch arm 16 being moved along the potentiometer to the end connectedto lead 14 so that control grids connected to lead 11 are at fullpotential.

When scene B is called for he moves the master switch arm I6 towards theend of the potentiometer connected to lead 13 and moves the masterswitch arm 6| towards the potentiometer end connected to lead 59, thusfading-in supply B and fading-out supply A. There is thus an overlappingof one control on the other, with supply B finally determining theillumination. However, the units which have their controlgridstconnected to be independent of the master switches I are notafiected by the change-over.

It will be understood that only two supplies A and B have been shown forthe sake of clearness, and that in the application of the invention inpractice many supplies are provided, and the scenes are preset beforethe time of a theater performance.

Thus, with flve supplies the operator may preset the controls for fivelighting effects and take advantage of the presetting in transferringthe grid lead of the tubes from one supply to another, or, obviously, inusing five tubes in parallel.

To illustrate some of the possibilities of only two supplies, we mayassume acondition in which scene A is in action with the footlights dim,the

border-lights out, and the pocket-light bright.

Scene B has been preset for footiights bright, border-lights dim, andpocket-light out.

One possibility is that scene A can be fadedout and scene B faded-inwith the resulting scene that for which B was preset.

Another possibility is that scene B can be faded-in without any changein the master switch of A. Now the result is, footlights bright,borderlights dim, and the pocket-light bright. So, the

presetting of scenes A and B actually enables the operator to preset forthree scenes or more, depending upon how he manipulates the two masterswitches. g

Of course, a further change can be made .in the scene by manipulatingthe control of any individual unit to fade-in or fade-out a light in agiven position, or by the manipulation of the controls of individualunits to produce a blending of colors. I

It will now be apparent that with a relatively small number of suppliesa great many different lightingbfiects may be obtained with but littleeffort on the part of the operator, and while the term scene has beenused herein for ease in description, it is to be understood that theterm is synonymous with lighting eifect, and that the 'variouspreselected lighting effects can be used singly and in combination invarious numbers and in any order to provide the required lighting forany part of a play or production.

An important advantage of the combination of instrumentalities describedwill now be pointed out. If it is assumed that the footlights are presetfor full brilliancy, the border-lights for threequarters brilliancy, andthe pocket-lights for half-brilliancy, then, upon movement of the masterswitch to control the scene, it requires full movement of the masterswitch from its initial to its final position, to obtain the desiredbrilliancy. Thus, starting from zero current it requires a full sweep ofthe master switch arm'to produce, respectively, full, three-quarters andhalf of full brilliancy on the controlled units. Again, movement of themaster switch arm from an initial position of zero current to a positionproducing half brilliancy in the footlights results in a brilliancy inthe other units which is substantially just half of that for which theothers were preset.

In other words, movement of the master switch arm produces proportionalintensity control of all connected units, regardless of the intensityfor which each unit was preset.

It should also be noted that with the system herein set forth lightingunits of various colors may be preselected, by presetting the controls,so that a desired resultant shade may be produced. For example, red andblue lighting units maybe used simultaneously to produce many shades ofviolet depending upon the comparative number of units of each color andthe intensities of the units. Then, with the master control all of thepreselected lighting units may be simultaneously dimmed or brightenedwithout color the various intensities for which the units have means forpreselecting the brilliancy of said .unit,

been preset will be varied proportionally by the mastercontrol.

It will also be undertsood that while a few results and the methods ofobtaining them with this invention have been above described; many morelighting etlects may be produced by manip'- ulations obvious from theforegoing to one skilled in the art.

I. am aware that many changes may be made and numerous detailsofconstruction may be varied through a wide range without departing fromthe principles of this invention, and I, therefore, do not purposelimiting the patent granted hereon otherwise than necessitated by theprior art.

I claim as my invention:

1. In a lighting control system, a lighting unit, a plurality of controlmeans normally connected for joint control of said unit, a plurality ofsupplies for controlling the energization of said control means, andmeans for selectively energizing said control means in parallel toselectively control the brilliancy of said lighting unit.

2. In a lighting control system, a lighting unit, a plurality of controlmeans having a' com'mon control over the brilliancy of said unit,supplies for controlling the energization of said control means, and avariable means in circuit with each control means for governing theeffect of that control means on said unit, whereby the effect of onecontrol means on the brilliancy of said unit may be reduced while theefiect of another control means is increased to produce overlapping ofbrilliancy control.

3. In a lighting control system, a lighting unit, a plurality ofparallel connected control means adapted for joint control of thebrilliancy of said unit, supplies for controlling the energization ofsaid control means, presettable and variable means in circuit with eachof said control said presettable means being adapted for concurrentcontrol of said unit whereby there may be an overlapping of brilliancycontrol and that control means preset for the higher brilliancy willdetermine the brilliancy of said unit.

4. In a lighting control system, a lighting unit,

a plurality of control means normally connected in parallel for jointcontrol of said unit, supplies for controlling the energization of saidcontrol means, and means'for selectively energizing said control means'to selectively control the brilliancy of said lighting unit.-

5. In a lighting control system, a lighting unit, a pluralityof controlmeans for said unit connected in parallel, means establishing a commonconnection between said parallel connected control means and said unitwhereby said control means are adapted for joint control of said unit,and means in. circuit with each of said thermionic tubes incircuitbetween said control means and said unit, whereby control of said unitmay be exercised through any of said tubes.

7'. In a lighting control system, a lighting unit,

,a reactance having control coil means in circuit with said'unit, aplurality of parallel connected thermionic tubes in series with saidcontrol coil means, and means in circuit with said tubes for controllingthe brilliancy of said unit through said tubes, whereby any one of saidtubes may be selectively used to control said unit. 7

- -8. In a lighting control system, a lighting unit, a plurality ofparallel connected thermionic tubes, common means connecting said tubeswith said unit, and a means in circuit with each trol means and saidtubes, and a common connection between said tubes and said unit, whereby said unit may be selectively controlled through any of said tubes.

10. In a lighting control system, a lighting cir- I cuit, a reactor insaid circuit .provided with a control winding, a plurality of parallelconnected rectifiers connected to said control winding to determine thecontrol current flowing therein, and means connected to selectively varythe m fluence of each of said rectifiers upon said 'control current. 4

11. In a lighting control system, a lighting circuit, a reactor in saidlighting circuit provided with a control winding, a plurality ofrectifier means connected todetermine the control current flowing insaid control winding, and means connected to selectively vary theinfluence of each of said rectifiers upon said control current.

12. An alternating supply system, a lightingv circuit connected to saidsystem, a reactor connected in said lighting}, circuit provided with acontrol winding, a plurality of parallel connected means connected todetermine the control current flowing in said winding, and meansconnected to said supply system and to said parallel connected means toselectively vary the influence of each of said parallel connected meansupon said control current.

13. -A lighting circuit, a reactor in said circuit provided with acontrol winding, a rectifier connected to said control winding, anotherrectifier, means connecting said rectifiers for common control ofcurrent in said control windin and means to selectively vary theinfluence of each of said rectifiers upon said control current.

14. A lighting circuit, a reactor in said circuit provided with acontrol winding, means to supply control current in said controlwinding, other means to supply current in said control winding, means inparallel to connect said supply means for joint control of the currentsupplied to said control winding, and means to selectively determine thecurrent supplied by each of said supply means. I

15. A lighting circuit, a reactor in said lighting circuit provided witha control winding, a pinrality of thermionic tubes connected to saidcontrol winding to vary the reactance of said reactor,

each of said tubes having a control electrode, a

plurality of sources of potential for the control electrodes of saidtubes, and control means connecting said sources of potential and saidcontrol electrodesior joint and selective control of said reactor bysaid potential sources.

16. A lighting circuit','-a reactor in said lighting circuit providedwith a. control winding, a plurality of sources of potential connectedin par 10 dimmer means to vary the light intensity of the lightingunits, and means to selectively inter-' connect said sources ofpotential for Joint control of said dimmer means.

18. A theatre lighting circuit, a reactor in said l circuit providedwith a control winding, current sources connected in parallel for jointcurrent supply to said control winding, means connect-- ing said currentsources with said control winding, and means to selectively vary thecurrent supplied by each of said current sources to said controlwinding.

19. In a theatre lighting system, a plurality of lightingcircuits,individualintensity control means for each circuit, mastercontrol means for simultaneous intensity control of said circuits, othermaster control means for simultaneous intensity control of saidcircuits, means to connect said master control means in parallel forjoint control of said circuits, and means to selectively vary saidmaster control means while they are so connected for joint control ofsaid circuits.

20. In a lighting circuit, intensity control means for said circuitcomprising parallel connected thermionic tubes for joint control of saidcircuit, each of said tubes having a control electrode, and meansconnected with said control electrodes to selectively aflect thecontrolling influence of each of said tubes upon said lighting circuit.

40 21. A lighting circuit, a reactor'in said circuit having a controlwinding, a current source for said control winding conditioned toproduce one intensity eiIect in said lighting-circuit, another currentsource for said control winding pre-set 45 conditioned to produceanother intensity effect in said lighting circuit, means to connect saidcurrent sources in parallel while so conditioned, and means to variouslycondition said current supplies while in parallel connection.-

50 22. A lightingv circuit, a reactor in said circuit having a controlwinding, a plurality of thermionic tubes in parallel connection, meansconnecting said parallel connected tubes to said control winding tocontrol current flow in said wind- 56 ing, each of said tubes having acontrol electrode, a plurality 01' potential sources for the controlelectrodes of said tubes, pre-settable means to condition'said potentialsources, and means to selectively switch said conditioned potential 0sources into connection with said control electrodes for joint andseveral control thereby of the -reactance of said reactor.

23. In a lighting control system, lighting cir- 24. In a lightingcontrol system, a plurality of lighting circuits, variable meansconnected for electrically controlling each circuit for presettingintensity of that circuit, master control means connectible with saidvariable means, and impedance compensating means in circuit with saidvariable means to maintain the impedance within desirable operatinglimits, whereby said master control is substantially constant ineffectiveness when in circuit with said variable means regardless of thesettings of said variable means.

.25. Ina lighting control system, a plurality of lighting circuits, asupply circuit for con-v trolling the energization of said lightingcircuits, a variable control means in said'supply circuit for eachlighting circuit, a master control in said supply circuit, and means insaid supply circuit to automatically maintain the impedancesubstantially constant to ensuresubstantially constant effectiveness ofsaid master control regardless of the settings of said variable controlmeans.

26. In a lighting control system, a plurality of lighting circuits, asupply circuit for controlling the energization of said lightingcircuits, saidsupply circuit including a variable control means for saidlighting circuits, at power line, a transformer between said line andsaid supply circuit, voltage control means in series with the secondaryof said transformer, and means in said supply circuit to maintain theimpedance of the circuit substantially constant.

27. In combination, in a theater lighting system, a plurality of groupsof control means including individual control means, a plurality oilighting circuits to be controlled respectively by individual controlvmeans of each group, said control means being each presettable inadvance to preselect a corresponding lighting circuit for subsequentenergization and predetermined brilliancy of said lighting circuit, amaster control for each group in circuit connection with the controlmeans of the respective group, current supply means for said controlmeans, current supply means for said lighting circuit, andloadcompensating means in circuit with said group control means adaptedto maintain a substantially constant effectiveness of said mastercontrol of said group regardless of the setting of said group controlmeans.

28. In a lighting system, a plurality of lighting circuits, currentsupply means, a plurality of control means each being presettable tocontrol the energization of a lighting circuit and the brilliancy ofsaid circuit, master control means for circuit connection with saidplurality of control means, means in circuit with each of said pluralityof control means for selective connection 01' said plurality of controlmeans to said current supply means directly or thorugh said mastercontrol means, respectively, and loadcompensating means automaticallyoperable to maintain a substantially constant eilectiveness of saidmaster control means regardless of the setting or connection of aplurality of said plurality of control means.

29. In combination, in an electrical system a pluralityoi lightingcircuits, a current source, supply lines connected to said currentsource, a group of control means connected to said supply lines, saidgroup including a plurality oi individuals each presettable to controlenergization of a lighting circuit, a master control for said group ofcontrol means and in circuit connection therewith, and means in circuitconnection with said individuals adapted to maintain a substantiallyconstant effectiveness of said master control in its control of saidgroup regardless of the setting of said individuals.

30. A lighting unit, a first control means, a second control meansconnected in parallel with said first control means, a pluralityof-current supplies for said control means, and means in circuit withsaid current supplies to vary the intensity of current supplied to saidcontrol means and thereby selectively transfer control of said unit fromone to the other of said control means.

31. A lighting unit, a plurality of control means connected in parallelfor joint control of said unit, current supplies connected in circuitwith said control means for the energization of said control means, andmeans in circuit with said current supplies to selectively vary theeffectiveness of said control means while maintaining the continuity ofthe supply circuits.

32. A lighting unit, a plurality of control control of said'unit, aplurality of current supplies connected energizing said control means,meansin said supply circuits presettable to selectively predetermineenergization of said con-' trol means, and a master control in circuitwith said presettable means for joint control of a plurality of saidcurrent supplies.

33. A lighting unit, a first control means connected to said unit, asecond control means connected to said unit and normally in parallelwith said first control means, a first current supply in circuit withsaid-first control means, a second current supply in circuit with saidsecond control means, and means in circuit with said .current suppliesto render a selected control means ineffective while maintaining thecontinuity of its supply circuit;

34. Alighting unit, a first control means connected to said unit, afirst current supply connected for energization of said first controlmeans, a second control means connected to said unit, a second supplycircuit connected for energization of said secondcontrol means, and

means to transfer control of said unit from said first control means tosaid second control means while maintaining the continuity of said firstand second supply circuits.

35. A lighting unit, a first control means connected to saidunit, afirst supply circuit connected for energization of said first controlmeans, means in circuit with said first supply I 5' means presettable todetermine the brilliancy of said unit, a second control means connectedto said unit, a second supply circuit connected for energization of saidsecond controlgmeans, means in said second'supply circuit presettable todetermine the brilliancy of said unit, and

means to transfer control of said unit from-one control means to theother by superimposing one v control means on the other whilemaintainingthe continuity of said supply circuits.

36. A lighting unit, a first control means co nected to said unit,afirst supply circuit connected for energization of said control meansand having means in circuitthei'ewlth adjusted to securea desired lowbrilliancy of. said unit, a second control means connected to said unit,a second supply circuit !orenergization of said second control means andhaving means in circult therewith presettable to secure a desired highbrilliancy of said unit, and means to .tain the desired shade.

impose said second control means on said first control means to secure ahigh brilliancy of said unit while maintaining said supply circuits intheir adjusted condition and while maintaining the continuity of saidsupply circuits.

37. A plurality of lighting units, a pair of sup- I ply lines, a mastercontrol connected in parallel to said lines, a conductor connected to avariable point on said master control, a plurality of pre-' means beingeach connected with a lighting unit I to vary the brilliancy of theunit, respectively,

whereby brilliancies preselected by said presettable means are variedproportionally upon movement of said conductor to selected points onsaid master control.

38. A plurality of lighting units, a pair of supply lines, a mastercontrol connected in parallel to said lines, a conductor connected to avariable point on said master control, a first roup of presettablevariable means connected to one of said supply lines and to saidconductor, a second group of presettable =variable means connected tosaid pair of supply lines, means for selectively connecting a lightingunit atwill to a variable means of one or the other of said groups ofpresettable means for control by the master or by an individual variablemeans, respectively, and load compensating means in circuit with saidconductor and with said first group of presettable variable means tocompensate for the load .imposed by the variable setting of saidvariable de-energize a selected control means while maintaining thecontinuity of its supply circuit.

40. An alternating current supply system, a power unit connected to saidsystem, a reactor in-series with said unit, said reactor being providedwith a control winding, a pair of current sources connected in parallelfor joint current supply to said winding, and means to transfer controlof said unit fromone to the other of said current sources whilemaintaining the continuity of the circuits connecting said sources andsaid winding.

41. In a lighting control system, a plurality of lighting circuitsincluding lighting units. combinable to produce colorsof desired shades,variable means in circuit withv each lighting circuit presettable todetermine in advance the shade desired from the respectivelightingcircuit, sup ply lines. a master control-connected with said supplylines and with said variable means, andcompensate for the load imposedby the variable setting of said variable means whereby movethebrilliancies of said lighting circuits to main- ALBERT R.

ment of said master control is effective to vary.

